The proposed research is designed to evaluate the development of relationship characteristics associated with sexual behaviors, relationship formation, exclusivity and relationship transition among middle and late adolescent women. Sexual activity occurs in the context of developmental changes in interpersonal relationships as well as the functions and meanings of sexual relationships within adolescence and in the transition to young adulthood. Data will be obtained from middle (ages 14 - 17 years) and late adolescent women (ages 18 - 20 years) at enrollment. The younger participants will be evaluated via self-administered questionnaire, face-to-face interview and daily diary for a period of 27-months. Late adolescents will be recruited from participants completing a 27-month study (funded by the National Institute of Allergy & Infectious Diseases) of factors associated with sexually transmitted infections (STI). Participants of the earlier study entered at ages 14 -17 years. The current project proposes to continue intensive data collection on sexual behavior and sexual relationships for an additional 27- month period. Thus, these data will reflect a full span of development encompassing middle and late adolescence and the transition into young adulthood. Several types of data - self-administer questionnaire, face-to-face interview - will be used. Coital diaries allow analytic focus on specific transitional coital events (i.e., coitus with a new sex partner). The statistical concept of 'runs' will be used to assess sequences of sexual events and transitions to new partners. Developmental trends in relationship formation, relationship quality, coital frequency and condom use will be assessed by latent growth curve analysis.